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Veterinary Medicine International
Volume 2012 (2012), Article ID 796527, 19 pages
Review Article

A Review of Hypothesized Determinants Associated with Bighorn Sheep (Ovis canadensis) Die-Offs

1P.O. Box 2786, Loveland, CO 80539-2786, USA
2U.S. National Parasite Collection, ARS, USDA Animal Parasitic Diseases Laboratory BARC, East 1180 10300 Baltimore Avenue, Beltsville, MD 20705, USA
3Caine Veterinary Teaching Center, College of Agriculture and Life Sciences, University of Idaho, 1020 East Homedale Road, Caldwell, ID 83607, USA
4Montana Fish Wildlife and Parks, 1400 South 19th Avenue, Bozeman, MT 59715, USA
5Wildlife Conservation Society, 2023 Stadium Drive, Suite. 1A, Bozeman, MT 59715, USA
6Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, USA
7Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA

Received 1 December 2011; Accepted 14 January 2012

Academic Editor: David W. Horohov

Copyright © 2012 David S. Miller et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Multiple determinants have been hypothesized to cause or favor disease outbreaks among free-ranging bighorn sheep (Ovis canadensis) populations. This paper considered direct and indirect causes of mortality, as well as potential interactions among proposed environmental, host, and agent determinants of disease. A clear, invariant relationship between a single agent and field outbreaks has not yet been documented, in part due to methodological limitations and practical challenges associated with developing rigorous study designs. Therefore, although there is a need to develop predictive models for outbreaks and validated mitigation strategies, uncertainty remains as to whether outbreaks are due to endemic or recently introduced agents. Consequently, absence of established and universal explanations for outbreaks contributes to conflict among wildlife and livestock stakeholders over land use and management practices. This example illustrates the challenge of developing comprehensive models for understanding and managing wildlife diseases in complex biological and sociological environments.